Create a new SlidingWindow data structure

Summary: Creates a new SlidingWindow data structure for general purpose use in stats code.

Reviewed By: anakryiko

Differential Revision: D7597047

fbshipit-source-id: 227438055029c2bacb5edf2943ebc9cc66fdfe36

CMakeLists.txt

@@ -632,6 +632,7 @@ if (BUILD_TESTS)
 
     DIRECTORY stats/test/
       TEST histogram_test SOURCES HistogramTest.cpp
+      TEST sliding_window_test SOURCES SlidingWindowTest.cpp
       TEST tdigest_test SOURCES TDigestTest.cpp
       TEST timeseries_histogram_test SOURCES TimeseriesHistogramTest.cpp
       TEST timeseries_test SOURCES TimeSeriesTest.cpp

folly/Makefile.am

@@ -439,6 +439,8 @@ nobase_follyinclude_HEADERS = \
 	ssl/detail/OpenSSLThreading.h \
 	ssl/detail/SSLSessionImpl.h \
 	stats/detail/Bucket.h \
+	stats/detail/SlidingWindow-defs.h \
+	stats/detail/SlidingWindow.h \
 	stats/BucketedTimeSeries-defs.h \
 	stats/BucketedTimeSeries.h \
 	stats/Histogram-defs.h \

folly/stats/detail/SlidingWindow-defs.h

+/*
+ * Copyright 2018-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <folly/stats/detail/SlidingWindow.h>
+
+#include <algorithm>
+
+namespace folly {
+namespace detail {
+
+template <typename BucketT>
+SlidingWindow<BucketT>::SlidingWindow(
+    Function<BucketT(void)> fn,
+    size_t numBuckets)
+    : fn_(std::move(fn)), curHead_(0) {
+  buckets_.reserve(numBuckets);
+  for (size_t i = 0; i < numBuckets; ++i) {
+    buckets_.push_back(fn_());
+  }
+  std::reverse(buckets_.begin(), buckets_.end());
+}
+
+template <typename BucketT>
+SlidingWindow<BucketT>::SlidingWindow(SlidingWindow<BucketT>&& rhs)
+    : fn_(std::move(rhs.fn_)),
+      buckets_(std::move(rhs.buckets_)),
+      curHead_(rhs.curHead_) {}
+
+template <typename BucketT>
+std::vector<BucketT> SlidingWindow<BucketT>::get() const {
+  std::vector<BucketT> buckets;
+  buckets.reserve(buckets_.size());
+  buckets.insert(buckets.end(), buckets_.begin() + curHead_, buckets_.end());
+  buckets.insert(buckets.end(), buckets_.begin(), buckets_.begin() + curHead_);
+  return buckets;
+}
+
+template <typename BucketT>
+BucketT SlidingWindow<BucketT>::slide(size_t nBuckets) {
+  nBuckets = std::min(nBuckets, buckets_.size());
+  for (size_t i = 0; i < nBuckets; ++i) {
+    if (curHead_ == 0) {
+      curHead_ = buckets_.size() - 1;
+    } else {
+      curHead_--;
+    }
+    buckets_[curHead_] = fn_();
+  }
+  return buckets_[curHead_];
+}
+
+} // namespace detail
+} // namespace folly

folly/stats/detail/SlidingWindow.h

+/*
+ * Copyright 2018-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <cstddef>
+#include <vector>
+
+#include <folly/Function.h>
+
+namespace folly {
+namespace detail {
+
+/*
+ * This class represents a sliding window that can be used to track stats over
+ * time. Buckets are dropped and new ones are added with the slide() method.
+ * New buckets are created with the constructor function given at construction.
+ */
+template <typename BucketT>
+class SlidingWindow {
+ public:
+  SlidingWindow(Function<BucketT(void)> fn, size_t numBuckets);
+
+  SlidingWindow(SlidingWindow&& rhs);
+
+  std::vector<BucketT> get() const;
+
+  /*
+   * Slides the SlidingWindow by nBuckets, inserting new buckets using the
+   * Function given during construction. Returns the new first bucket.
+   */
+  BucketT slide(size_t nBuckets);
+
+ private:
+  Function<BucketT(void)> fn_;
+  std::vector<BucketT> buckets_;
+  size_t curHead_;
+};
+
+} // namespace detail
+} // namespace folly

folly/stats/test/Makefile.am

@@ -5,12 +5,16 @@ ldadd = $(top_builddir)/test/libfollytestmain.la
 
 TESTS = \
 				histogram_test \
+				sliding_window_test \
 				tdigest_test
 
-TESTS = $(check_PROGRAMS)
+check_PROGRAMS = $(TESTS)
 
 histogram_test_SOURCES = HistogramTest.cpp
 histogram_test_LDADD = $(ldadd)
 
+sliding_window_test_SOURCES = SlidingWindowTest.cpp
+sliding_window_test_LDADD = $(ldadd)
+
 tdigest_test_SOURCES = TDigestTest.cpp
 tdigest_test_LDADD = $(ldadd)

folly/stats/test/SlidingWindowTest.cpp

+/*
+ * Copyright 2018-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/stats/detail/SlidingWindow-defs.h>
+
+#include <folly/portability/GTest.h>
+
+using namespace folly;
+using namespace folly::detail;
+
+class SlidingWindowTest : public ::testing::Test {
+ protected:
+  std::unique_ptr<SlidingWindow<size_t>> slidingWindow;
+  size_t curWindow = 0;
+
+  void SetUp() override {
+    slidingWindow = std::make_unique<SlidingWindow<size_t>>(
+        [&]() { return curWindow++; }, 60);
+  }
+};
+
+TEST_F(SlidingWindowTest, Constructor) {
+  auto buckets = slidingWindow->get();
+  EXPECT_EQ(60, buckets.size());
+
+  for (size_t i = 0; i < 60; ++i) {
+    EXPECT_EQ(60 - i - 1, buckets[i]);
+  }
+}
+
+TEST_F(SlidingWindowTest, SlideZero) {
+  slidingWindow->slide(0);
+  auto buckets = slidingWindow->get();
+  EXPECT_EQ(60, buckets.size());
+
+  for (size_t i = 0; i < 60; ++i) {
+    EXPECT_EQ(60 - i - 1, buckets[i]);
+  }
+}
+
+TEST_F(SlidingWindowTest, SlideLessThanFullAmount) {
+  slidingWindow->slide(5);
+  auto buckets = slidingWindow->get();
+  EXPECT_EQ(60, buckets.size());
+
+  for (size_t i = 0; i < 60; ++i) {
+    EXPECT_EQ(65 - i - 1, buckets[i]);
+  }
+}
+
+TEST_F(SlidingWindowTest, SlideMoreThanFullAmount) {
+  slidingWindow->slide(60);
+  auto buckets = slidingWindow->get();
+  EXPECT_EQ(60, buckets.size());
+
+  for (size_t i = 0; i < 60; ++i) {
+    EXPECT_EQ(120 - i - 1, buckets[i]);
+  }
+}